CONAKRY, Guinea — Guinea’s government said Tuesday that it would investigate why troops opened fire on protesters at a pro-democracy rally. A human-rights group said 157 people were killed and more than 1,000 were injured.

While saying it would investigate, the government continued to maintain that the protest was illegal. It also said far fewer people died than reported.

Hospitals were flooded with patients Tuesday, and the death toll rose through the day.

Presidential guard troops fired on 50,000 people at the main football stadium Monday, shattering hopes that this West African country was shedding the yoke of dictatorship.

Some of those at the rally, upset that a military officer who seized power in a December coup might run for president in January elections, had chanted: “We want true democracy.”